Many people mention heart in training more metaphorical as intention, intensity, and commitment.

OYOH, our body is a neuro-network that beats, and breathes, and functions without conscious attention, thought, or direction.

We talk about muscle-memory and the heart is a muscle that can be developed.

I read an article the other day about the difference in brain activity between a powerful karate punch by a black belt versus brain activity from a beginner.

I often read about neuro-science studies in mental health.

I think we will find more as neuro-sciences studies move forward.

Thanks for answering, I guess the topic is very diverse and my questions are not really specific..
At one point I couldnīt get a specific opening right during a paired aikiken kata, and I was told to use the heart for that particular opening. It made perfect sence on an intuitive level, and worked well, so I guess I am just trying to look for an explanation of some sort.. hmm.
Cheers !